Patricia Ferguson, Scottish Labour constitutional spokesman, condemned Mr Berry’s comments, saying: “To suggest the people of Scotland are slaves is insulting, not least to those who fought in two world wars to ensure we enjoy the freedom we do.”

Mr Berry was council leader in East Lothian between 2007 and 2010, when he stood down to concentrate on winning the local Scottish Parliament seat.

In the following year’s election, he came close to beating Iain Gray, then the Scottish Labour leader, as the SNP won a landslide victory.

He made the remarks in response to a tweet from Better Together, the anti-separation referendum campaign, stating it has produced a new leaflet stating why Scots think they are stronger in the UK.

“Do you have equivalent quotes from abused women saying why they don't need a divorce or slaves happy on the plantation, Massah?” he asked.

When the taste of his comments was criticised, he responded: “If a woman's dowry included £60 billion pa (per annum) in oil revenue and her partner squandered it on the own priorities, is that not abuse?”

In a third tweet, he added: “If a distant master foists appalling weapons on a part of his domain against the express will of the people is that not slavery?”

Mr Berry denied trivialising slavery or domestic abuse but eventually posted a final tweet stating: “In view of strong response, my original comments seem excessive. I withdraw them and apologise if I caused offence.”

Meanwhile, the country scheduled to assume the EU presidency shortly after the referendum has confirmed a separate Scotland would have to apply from scratch for membership.

Edgars Rinkevics, the Latvian foreign minister, told the BBC Scotland would be considered a “new country” and would have to go through the full accession process.

However, he also raised the possibility that the rest of the UK might not automatically inherit membership and disclosed the European Commission was "considering" that question.